I have a Smart TV and was trying to watch it through the MLB app on there. Although I still had same issue when trying to watch it on my laptop as well so who knows.
After issues with the game being blacked out the last two nights (even though I have Cardinals.TV and haven't had issues with other Cards/Cubs games this season), I was finally able to watch tonight's game and not have to rely just on the radio broadcast.
So even though I have Cardinals.TV, I am apparently blacked out because this game is also airing on Marquee. This legit has not happened for any of the other games with these two teams this season in this situation. And I'm in Springfield so there shouldn't be an issue with watching it.